This invention relates to a pressure gage that can be used in various environments to measure the peak overpressure of pressure transients in various media over a continuous and wide range of pressures.
Diaphragm pressure gages are well known in the art. Such gages provide a convenient and inexpensive method to measure the peak overpressure due to explosions in air, or other forms of pressure transients, occurring too rapidly to follow or be followed by static pressure devices such as manometers or that must be monitored remotely due to hazards presented by the explosive environment. These devices are frequently employed where electronic pressure transducers are not available, where the environment is not conducive to the use of electronic devices, where a back-up measuring instrument is desired to assure a reading in the event of the failure of the electronic device, where there is a desire to verify the validity of the pressure gage signals be means of a direct mechanical effect produced by the presence of pressure transients, or where there exists the possibility of spurious effects producing false signals as frequently happens with electronic gages.
Prior art diaphragm overpressure gases have employed a device consisting of a rigid flat plate having a shallow cylindrical air cavity covered by a metal sheet, usually aluminum foil of uniform thickness. When exposed to a shock or blast pressure pulse of sufficient intensity, the foil will rupture. For a cylindrical cavity of a given diameter and foil of uniform thickness and properties, the overpressure at which rupture occurs is reproducible. Thus, the device can be used to determine whether the transient being measured exceeded or failed to exceed the particular discreet rupture overpressure of its design.
By using several of these prior art discrete pressure measuring diaphragm gages of varying cavity diameter and/or foil thickness, it is possible to bracket the value of the pressure to be measured. The use of a diaphragm gage that ruptures at pressure P1 together with a second that ruptures at a pressure P2, where P2 is greater than P1, in a single measurement event can establish whether or not pressure at these two gates have a peak overpressure value between P1 and P2. By adding more and more of these discrete pressure mounting diaphragm gages, it is possible to obtain greater precision. In the prior art, the number of cavities required, however, becomes excessive if precision in the measurement is to be achieved. Moreover, as the number of these cavities increases, the area that they cover becomes a significant impediment to efforts to obtain valid measurements, because the pressure can vary from point to point in the vicinity of the position where a pressure measurement is desired.
The continuous measuring diaphragm pressure gage or non-discrete diaphragm pressure gage of the present invention differs from the prior art in that it combines the features of a yielding diaphragm gage without rupture and a discrete diaphragm pressure gage where pressures are determined by the rupture of the diaphragms. The continuous measuring diaphragm pressure gage also differs from the prior art in that it replaces the cylindrical cavity behind the foil of the discrete diaphragm pressure gage in the prior art with a cavity having a wedge-shape, that is a cavity that has walls that vary the cavity width in a gradual manner from a narrow width to a wide width. In the preferred embodiment the cavity consist of two cylindrical sections cut across the cylinder diameter, one of large radius and one of small radius, joined by a wedge-shaped cavity section. However, any elongated cavity that has two opposing sides with edges sloping away from one another can be employed. This cavity is covered by a uniform foil sheet of metal or other deformable material. In the preferred embodiment this foil is secured in place by means of a cover plate having a cut-out pattern matching the cavity behind the foil so that a pressure pulse incident on the device will have unimpeded access to the foil covering the cavity. The cover plate can be calibrated for the pressure pulse magnitude by means of markings on the cover plate providing a reference by means of which the extent of rupture of the foil is measured along the axis of the cover plate opening.
Another important limitation of the prior art diaphragm pressure gage is that it is sensitive to the shock or blast wave form.